Raise if ForeignKeyConstraint created with different numbers of

local and remote columns.

An :class:`.ArgumentError` is now raised if a
:class:`.ForeignKeyConstraint` object is created with a mismatched
number of "local" and "remote" columns, which otherwise causes the
internal state of the constraint to be incorrect.   Note that this
also impacts the condition where a dialect's reflection process
produces a mismatched set of columns for a foreign key constraint.

Downstream DB2 dialect has been reported as potentially causing this
scenario.

Change-Id: Id51c34a6c43749bb582639f9c1dc28723482f0e5
Fixes: #3949
References: #3998

1 files changed, 23 insertions, 0 deletions

diff --git a/test/sql/test_metadata.py b/test/sql/test_metadata.py
index 6d0df3b5f..61fbbc57b 100644
--- a/test/sql/test_metadata.py
+++ b/test/sql/test_metadata.py
@@ -348,6 +348,29 @@ class MetaDataTest(fixtures.TestBase, ComparesTables):
             getattr, list(a.foreign_keys)[0], "column"
         )
 
+    def test_fk_mismatched_local_remote_cols(self):
+
+        assert_raises_message(
+            exc.ArgumentError,
+            "ForeignKeyConstraint number of constrained columns must "
+            "match the number of referenced columns.",
+            ForeignKeyConstraint, ['a'], ['b.a', 'b.b']
+        )
+
+        assert_raises_message(
+            exc.ArgumentError,
+            "ForeignKeyConstraint number of constrained columns "
+            "must match the number of referenced columns.",
+            ForeignKeyConstraint, ['a', 'b'], ['b.a']
+        )
+
+        assert_raises_message(
+            exc.ArgumentError,
+            "ForeignKeyConstraint with duplicate source column "
+            "references are not supported.",
+            ForeignKeyConstraint, ['a', 'a'], ['b.a', 'b.b']
+        )
+
     def test_pickle_metadata_sequence_restated(self):
         m1 = MetaData()
         Table('a', m1,